WO2019038503A1 - Modified acoustic secondary nozzle - Google Patents

Abstract

An assembly for the rear of a bypass turbomachine (10) comprises a primary nozzle (11) comprising a trailing edge defining a primary flow path portion and a secondary nozzle (110) defining a secondary flow path portion, defined about a longitudinal axis (X), said secondary nozzle being configured to eject a mixture of the flows coming from a secondary flow path (Vs) and from a primary flow path (Vp) of the turbomachine (10), the secondary nozzle being of convergent–divergent shape with a throat (112) corresponding to a minimum cross section of the nozzle (110), the secondary nozzle (110) comprising, at the throat (112), a periodic succession of lobes (116, 118) which are situated along the internal circumference of the secondary nozzle (110). The assembly also comprises a lobed mixer (130) at the downstream end of the primary nozzle (11), this having an alternation of hot lobes (134) extending inside the secondary flow path and of cold lobes (132) extending inside the primary flow path. The lobes of the nozzle (110) which are concave (118), which is to say radially towards the outside, and respectively which are convex (116), which is to say radially towards the inside, if the longitudinal offset is disregarded, radically face the respectively hot lobes (134) and cold lobes (132) of the mixer (130).

Description

 Acoustic modified secondary nozzle

TECHNICAL FIELD GEN ERAL The present invention relates to the field of noise reduction for a mixed flow turbomachine. It relates more particularly to the rear body of a turbojet engine with a mixer, where the primary flow at the output of the engine and the secondary flow mix inside a so-called secondary nozzle, to form a jet propelled into the external air. .

The field of turbomachines concerned is thus relative to LDMF nozzles ("long duct mixed-flow"), that is to say a secondary nozzle extending beyond the mixture of flows.

The invention relates in particular to solutions to acoustics problems in the context of secondary convergent-divergent nozzle. STATE OF THE ART

In the context of so-called convergent-divergent nozzles, a source of noise comes from the fact that a Mach pocket is present at the neck of the nozzle.

Indeed, the interaction between the turbulence resulting from the mixing of the two streams and the supersonic flow zones in the nozzle is a source of high frequency noise. This phenomenon can occur especially when the nozzle begins to prime.

This phenomenon is more clearly observed when a lobe mixer is installed at the confluence of the primary and secondary flows. Referring to the applications FR2902469 or EP1870588 for the mixers, as well as WO2015 / 036684 which proposes a solution using chevrons located on the trailing edge of the nozzle.

However, the present invention is in the context of so-called convergent-divergent nozzles. The latter make it possible to improve the performance of the mixed flow nozzles, in particular by increasing the size of the convergent-divergent (called ratio "CVDC" and classically referenced A9 / A8 - see FIG. 1, which illustrates a nozzle 110, an edge of leak 114 and a neck 112 and the respective sections Sf / S _c ). A convergent-divergent nozzle, by definition, has a minimum section whose axial positioning does not coincide with one of the ends of the duct. The use of a convergent-divergent secondary nozzle has two advantages: it makes it possible to substantially modify the coefficient of flow with a low expansion ratio and to improve the performance of the nozzle. This increase is beneficial for the performance of the engine but it is damaging acoustically.

As indicated above, the appearance of a Mach pocket is observed at the neck (see FIG. 2, where the two curves represent the noise with mixer in solid line and without mixer in dashed line - in abscissa the frequency F and in ordered sound pressure level SPL for Sound Pressure Level, in decibel). The turbulence resulting from the mixing of the two streams and the Mach pocket causes the appearance of unwanted noise.

PRESENTATION OF THE INVENTION

The invention aims to reduce the aforementioned acoustic consequences in the context of convergent-divergent nozzle with mixer.

For this purpose, the invention proposes a secondary nozzle for a double-flow turbomachine, defined around a longitudinal axis, said nozzle being configured to eject a mixture of flows from a secondary vein and a primary vein of the turbomachine, the secondary nozzle being of convergent-divergent shape with a neck corresponding to a minimum section of the nozzle,

wherein the secondary nozzle comprises, at the neck, a periodic succession of lobes located along the inner circumference of the secondary nozzle.

The invention may include the following features, taken alone or in combination:

the periodic succession is such that the section of the nozzle at the neck is the smallest section of the nozzle,

 the radius at the trailing edge is greater than the maximum radius at the neck,

 the mean radius of the nozzle in the section at the neck corresponds to the equivalent radius of an equivalent circular section, so that the section of the nozzle at the neck is the smallest section of the nozzle,

 each lobe extends axially on a portion of the secondary nozzle a certain distance upstream and / or downstream of the neck, preferably downstream to the trailing edge of the nozzle,

 said distance is less than once the mean diameter of the nozzle at the neck,

 in sections orthogonal to the longitudinal axis, the amplitude of the lobes between successive sections along the upstream and / or downstream direction of the neck gradually decreases to be zero,

 the periodic succession of lobes is defined, at least over a portion of the internal circumference, preferably more than 75% of the internal circumference, by the following equation:

R (x, Θ) = R _ref (x) + L (x). cos (N Θ)

où R est le rayon de la tuyère secondaire en fonction de la position circonférentielle et de l'abscisse le long de l'axe longitudinal de la tuyère, Xcoi est l'abscisse du col, R_ref est le rayon d'un section circulaire de référence, L est une fonction d'amplitude dépendant de l'abscisse, N est le nombre de périodes, and

where R is the radius of the secondary nozzle as a function of the circumferential position of the abscissa and along the longitudinal axis of the nozzle, Xcoi is the abscissa of the cervix, R _ref is the radius of a circular section reference, L is an amplitude function depending on the abscissa, N is the number of periods,

 the lobes are formed directly in the material of the nozzle,

- The ratio between the section at the trailing edge of the secondary nozzle and the neck section of the secondary nozzle is between 1 and 1.05. The invention also relates to a turbomachine rear assembly having a longitudinal axis, comprising:

 a secondary nozzle as defined above, defining a portion of secondary vein,

 a primary nozzle, comprising a trailing edge and defining a portion of primary vein,

 - a lobe mixer, at the downstream end of the primary nozzle and having an alternation of hot lobes extending inside the secondary vein and cold lobes extending inside the primary vein,

wherein the concave lobes, respectively convex, of the nozzle are, at the longitudinal shift, radially opposite the hot lobes, respectively cold, of the mixer.

Each vertex of the mixer lobes may be radially aligned, with a longitudinal offset, with a vertex of a lobe of the nozzle.

 There may be as many concave lobes as hot lobes and as many convex lobes as cold lobes.

The invention also relates to a dual-stream turbomachine comprising a nozzle as described above or an assembly as described above.

PRESENTATION OF FIGURES Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which:

 FIG. 1 illustrates the general principle of a convergent-divergent nozzle,

 FIG. 2 illustrates noise spectra (in decibels) of a turbomachine with and without a lobe mixer,

 FIG. 3 illustrates in three dimensions an embodiment of the invention,

 FIG. 4 illustrates, by bringing back several elements in the same plane, an embodiment of the invention,

 - Figures 5 and 6 illustrate a nozzle according to the invention compared to a reference nozzle.

DETAILED DESCRIPTION

The invention will now be described in relation with FIGS. 3 to 6. The turbomachine rear body 100 concerned belongs to a double-flow turbomachine 10, comprising a primary vein Vp and a secondary vein Vs. We will speak of vein for the volume through which a flow flows. In the primary vein Vp thus circulates the primary flow and in the secondary vein Vs thus circulates the secondary flow.

The turbomachine 10 is arranged around a longitudinal axis X. The abscissa is defined as the position along this longitudinal axis X.

Within the primary vein Vp, the turbine engine 10 comprises conventional elements known to those skilled in the art, such as one or more compression stages, a combustion chamber and finally one or more stages of turbines, which in particular drive the compressors and also a fan, which allows to feed the secondary vein Vs and provides the bulk of the thrust. At the downstream end, the primary vein Vp is defined by a primary nozzle 11, which allows the ejection of the primary flow. The primary nozzle 11 may be formed of several different parts.

In the same way, within the secondary vein Vs, the turbomachine 10 incorporates conventional elements known to those skilled in the art. In particular, at the downstream end, the secondary vein is defined by a nozzle 110, called secondary nozzle. In the case of LDMF turbomachines, it extends downstream beyond the primary nozzle 11. Consequently, the secondary nozzle 110 ejects the secondary flow, mixed with the primary flow.

This secondary nozzle 110 is convergent-divergent. As indicated in the introduction, this means that the radius (or diameter) of the nozzle decreases and then rises again, in the flow direction of the flow. The direct consequence is that the flow section decreases and then increases again.

The "neck" 112 of the secondary nozzle is the part of the nozzle 110, at an abscissa x _CO i, where this section is minimal.

The convergence-divergence ratio is typically between 100% and 105% (ratio of the section at the trailing edge 114 on the section at the neck 112

The turbomachine rear body 100 may further comprise a central body 12 limiting the radial extension of the primary stream inside the nozzle 110. This central body 12 is not concerned by the invention. It is located on the longitudinal axis X and usually stops after a trailing edge 120 of the nozzle.

The primary nozzle 11 thus comprises a trailing edge 120 at an abscissa x _p upstream of the abscissa x _CO i. The central body 12, if present, extends beyond the longitudinal edge of the trailing edge 120, that is to say downstream of the abscissa x _p .

As illustrated in FIGS. 3 to 4, the primary nozzle 11 ends with a lobed mixer 130 whose function, as indicated in the introduction, is to mix the primary and secondary flows before it is completely ejected from the secondary nozzle. 110. With reference to FIG. 3, the lobe mixer 130 is a profiled piece extending inside the secondary nozzle 110, the walls defining inside the primary vein Vp and outside the secondary vein Vs. Mixers may have symmetrical and periodic lobes, or non-symmetrical and / or non-periodic lobes. The thickness of the trailing edge of the mixer 130, coinciding with the trailing edge 120 of the primary nozzle 11, is generally small to avoid a base effect between the two flows. The lobe mixer 130 generally stops at a significant distance from the downstream end of the nozzle 110 to allow the flow mixture to homogenize. It is recalled that the invention is placed in the framework of turbomachines LDMF ("long duct - mixed flow"). As can be seen in FIGS. 3 and 4, an exemplary embodiment of the mixer 130 is constituted by symmetrical, periodic azimuth lobes around the longitudinal axis X. In this example, the trailing edge line 120 has a shape three-dimensional corrugated in azimuth and regular periodically passing through a low point 132 of minimum radius and a high point 134 of maximum radius. The shape of the mixer is preferably obtained by joining this trailing edge line 120 by smooth smooth surfaces, on one side to the circular section of the outer wall of the primary nozzle 11, on the other side to the circular section of the secondary vein inner wall Vs. Known means enable those skilled in the art to obtain these smooth surfaces by defining regular radius variation laws to join the inlet sections to the trailing edge 120 of the lobed mixer 130 . In the example presented, the evolutions of the trailing edge 120 of the mixer 130 are periodic. In this way, the average surface between the radially outer wall and the radially inner wall of the mixer 130 makes periodic undulations in azimuth about the longitudinal axis X which create, on the side of the primary flow under the high points 134 of the trailing edge 120, diverging lobes (so-called hot lobes and referenced 134 for simplification), and create, on the side of the secondary flow above the low points 132 of the trailing edge 120, convergent lobes (called cold lobes and referenced 132 for simplification) .

In the example presented, the abscissa x _p on the longitudinal axis X which determines the maximum extension of the downstream lobe mixer 6 corresponds to the high points of the hot lobes (FIG. 3). By the abscissa x _p passes an ejection plane, that is to say a plane from which the flow of air is ejected from the hot lobes. This embodiment of the mixer comprises eighteen hot lobes symmetrical about the axial plane passing through their middle and distributed periodically.

In another embodiment of the invention, it is conceivable to define a lobe mixer 130 by modifying its axial extension, the penetration rate of the lobes (determined essentially by the rays of the high points 134 and 132 of the trailing edge). 120), the shape of this trailing edge 120, as well as the number of lobes. The lobes may also have no axial planes of symmetry. Likewise, although the distribution of the lobes is essentially periodic, this periodicity can be locally affected by modifying the shape of certain lobes, for example to adapt the mixer 130 to a pylon passage. The lobe mixer 130 promotes the mixing of the primary Vp and secondary Vs flows in the vein inside the secondary nozzle 110, in particular by causing shears and vortices at the interface between the streams. Now that the general framework has been described, the means of the invention will be explained in relation to FIGS. 3 to 6. The secondary nozzle 110 comprises, along its internal circumference, at the level of the neck 112, a periodic succession radially inwardly of lobes 118 radially inward 116. In other words, a periodic succession of lobes 116, 118 is provided on the inner circumference of the secondary nozzle 110. The succession comprises an alternation of convex lobes 116 and concave 118. This makes it possible to increase and decrease locally the radius of the neck 112 of the secondary nozzle 110 in particular, to allow a better distribution of the heat exiting the hot lobes. In particular, this makes it possible to keep the flow of air passing through the Mach pocket or pockets located at the neck 112, close to the inner wall of the nozzle 110. It is therefore a passive system.

The maximum radius of the secondary nozzle 110 at the neck 112, however, remains less than the radius of the secondary nozzle 110 at the trailing edge.

The lobes 116, 118 are preferably located over the entire inner circumference of the nozzle 110. However, it is possible that, for design reasons (asymmetry of revolution, passage of arms), certain portions of the circumference may be deprived of lobes. 116, 118.

The terms "convex" and "concave" mean "globally convex" and "globally concave", ie a lobe (which is a rounded portion) in which the material extends radially inward and a lobe in which material is recessed radially outwardly. It can locally have a convexity in the concavity. In other words and in a more general way, the nozzle presents at the neck a non-circular section, having an alternation of lobes so that the radius of the section varies regularly.

In a particular embodiment, the definitions of "convex" and "concave" can be strict, in that the convex lobes are defined by a convex curve (without inflection) and the concave lobes are defined by a concave curve. (without inflection, therefore). We will then speak of "strictly convex" and "strictly concave". In one embodiment, it is possible to have strictly concave lobes and convex lobes, according to the definitions explained above.

Compared to a conventional nozzle, whose sections orthogonal to the longitudinal axis X are circular, the area of the nozzle at the neck 112 remains preferably unchanged. This implies that, from an axisymmetric reference nozzle, of radius R _re f at the abscissa x _CO i corresponding to the neck 112, the concave lobes 118 extend radially outside the reference circular section and the convex lobes 116 extend radially inside the circular reference section (see FIGS. 5 and 6 - on the latter, R _ref is the circumference of the circular reference section).

The lobes 116, 118 of the secondary nozzle 110 are positioned circumferentially according to the cold 132 and hot 134 lobes of the mixer 130. In particular, the concave lobes 118 are positioned radially opposite the hot lobes 134, with the longitudinal shift close. Preferably, for obvious reasons of symmetry, the lobes of a concave / hot or convex / cold lobe pair are radially aligned (i.e., in an orthogonal section, the longitudinal axis and the two vertices). are aligned). Preferably, the sequence between a concave lobe 118 and a convex lobe 116 is in the radial alignment of the sequence between a hot lobe 134 and a cold lobe 132. For reasons of efficiency, in one embodiment, There are as many concave lobes 118 as hot lobes 134. In a complementary or alternative embodiment, there are as many convex lobes 118 as cold lobes 132. The numbers may not correspond in certain specific cases where constraints impose to remove a concave or convex lobe (actuator, etc.).

The lobes 116, 118 also extend longitudinally in the secondary nozzle 110 at a certain distance D from the neck, so as to generate aerodynamic shapes, whether upstream and / or downstream of the neck 112.

 For this, we prefer the amplitudes of the convex 116 and concave lobes 118 between several orthogonal sections to the longitudinal axis X successive which gradually decrease to become zero, upstream and downstream of the neck 112. This may mean that the section of the nozzle becomes generally circular. The decrease in the amplitude of the lobes is both absolute (the lobes outside the neck 112 have an amplitude lower than that at the neck level 112) and in relative (the amplitude of the lobe with respect to the diameter is greater at cervical level than elsewhere).

Preferably, the lobes 116, 118 are longitudinally centered on the neck 112 and therefore extend longitudinally upstream and downstream.

In one embodiment, the lobes 116, 118 extend to the trailing edge 114, with a gradually decreasing amplitude so that the trailing edge section 114 is circular. The distance D may depend on various parameters, such as in particular the distance between the trailing edge 114 and the collar 112. However, the distance between the neck 112 and one of the ends of the lobe 116, 118 is preferably less than 1 times the diameter of the secondary nozzle 110 at the neck 112.

In a particular embodiment adapted to a periodic mixer 130, the lobes define a sinusoid satisfying the following equation:

R (x, Θ) = R _ref (x) + L (x). cos (N Θ)

where R is the radius of the nozzle as a function of the circumferential position and the abscissa along the longitudinal axis of the nozzle, x _CO i is the abscissa of the neck, Rref is the radius of the circular reference section , L is a function of amplitude depending on the abscissa x, and N is the number of periods, that is to say the number of convex lobes 116 or concave 118 desired.

Since it is desired that the area of the section of the nozzle 110 at abscissa Xcoi be identical to that of the reference nozzle, the lobes also satisfy the following equation:

 The L function determines the evolution of the lobes according to the abscissa. In one embodiment, a Gaussian function is used.

In this embodiment, therefore, there are strictly convex and strictly concave lobes, centered longitudinally around the neck 112. The shape of the lobes of the nozzle 110 may derogate locally from the formula given to allow the passage of a pylon or dome. a structural tree. Thus, the formula can be applied for lobes on a portion of the inner circumference. This portion then extends at least 50% or 75% of the total internal circumference. In the absence of a particular structure that disturb the application of the formula, the entire circumference can be defined in this way. The lobes 116, 118 are preferably formed directly in the material of the nozzle, either during the foundry or by posterior deformation. It may be envisaged to create the convex lobes 116 by adding material after the manufacture of the secondary nozzle 110.

This modified nozzle has a limited mass impact, or even zero. Being passive, the risk of failure is also limited or even zero, and it consumes no additional resources. In addition, it does not reduce the treatment surface for known acoustic treatments (arranged in the thickness of the secondary nozzle). Finally, this modified nozzle involves almost no constraint on the architecture of conventional convergent-divergent nozzles. An increase in the temperature locally of 50 ° K allows for example to lower the Mach between 0.90 and 0.95, compared to a Mach of 1 for a temperature of 320 ° K.

The distorted nozzle 110 makes it possible to gain up to 1 cumulative EPNdB.

Claims

claims A turbomachine rear assembly (10) having a longitudinal axis (X), comprising:  a primary nozzle (11), comprising a trailing edge (112) and defining a portion of primary vein (Vp),  a secondary nozzle (110) defining a secondary vein portion (Vs), said nozzle being configured to eject a mixture of streams from a secondary vein (Vs) and a primary vein (Vp) of the turbomachine (10); ), the secondary nozzle being of convergent-divergent shape with a neck (112) corresponding to a minimum section of the nozzle (110),  - a lobe mixer (130) at the downstream end of the primary nozzle (11) and having an alternation of hot lobes (134) extending inside the secondary vein (Vs) and cold lobes (132) extending inside the primary vein (Vp), characterized in that  the secondary nozzle (110) comprises, at the neck (112), a periodic succession of lobes (116, 118) located along the internal circumference of the secondary nozzle (110), and  - The concave lobes (118), that is to say radially outwardly, respectively convex (116), that is to say radially inwardly, of the nozzle (110) are, at the longitudinal shift close radially facing the hot lobes (134), respectively cold, of the mixer (130). The turbomachine rear assembly (10) according to claim 1, wherein each lobe (116,118) extends axially over a portion of the secondary nozzle (110) at a distance (D) upstream and / or downstream of the neck (112), preferably downstream to the trailing edge (114) of the nozzle (110). The turbomachine rear assembly (10) according to claim 2, wherein the distance (D) is less than one times the average diameter of the nozzle (110) at the neck (112). The turbomachine rear assembly (10) according to claims 2 or 3, wherein, in sections orthogonal to the longitudinal axis (X), the amplitude of the lobes (116,118) between successive sections along the direction upstream and / or downstream of the neck (112) gradually decreases to be zero. The turbomachine rear assembly (10) according to any one of the preceding claims, wherein the periodic lobe succession is defined, at least over a portion of the inner circumference, preferably more than 75% of the inner circumference, by the following equation: R (x, Θ) = R _ref (x) + L (x). cos (N Θ) and nR ² _ref ( _xcoll ) = πR ² ( _xcc , e) dQ where R is the radius of the secondary nozzle as a function of the circumferential position and the abscissa along the longitudinal axis of the nozzle, Xcoi is the abscissa of the cervix, R _ref is the radius of a circular section of reference L is an amplitude function depending on the abscissa, N is the number of periods. The turbomachine rear assembly (10) according to any one of the preceding claims, wherein the lobes are formed directly in the nozzle material. The turbomachine rear assembly (10) according to any one of the preceding claims, wherein the ratio between the trailing edge section (114) of the secondary nozzle (110) and the neck section (112) of the secondary nozzle (110) is between 1 and 1.05. The turbomachine rear assembly (10) according to any one of the preceding claims, wherein the section of the trailing edge (114) of the secondary nozzle is circular. 9. The assembly of claim 8, wherein there are as many concave lobes (118) as hot lobes (134) and as many convex lobes (116) as cold lobes (132). 10. A double-flow turbomachine (10) comprising a nozzle according to any one of claims 1 to 7 or an assembly according to claims 8 and 9.